Analytic detection of biomolecules, e.g., proteins, nucleic acids, and the like, is fundamental to molecular biology. In many applications, it is desirable to detect the presence of one or more particular molecules in a sample. For example, identification of a particular DNA sequence within a mixture of restriction fragments is used to determine the presence, position, and number of copies of a gene in a genome. It is also an integral technique in DNA typing. Analytic detection is also used, e.g., in disease diagnosis and drug development, to determine the presence of a particular antibody or protein, e.g., in a blood sample or large chemical library. Detection of biomolecules is therefore of fundamental value in, e.g., diagnostic medicine, archaeology, anthropology, modern criminal investigation, and the like. To meet these needs many techniques, e.g., DNA blotting, RNA blotting, protein blotting, and ELISA assays, have been developed to detect the presence of a particular molecule or fragment in the midst of a complex sample containing similar molecules.
For example, western blotting is useful for detecting one or more specific proteins in a complex protein mixture, such as a cell extract. The procedure involves fractionating the protein mixture, typically by denaturing polyacrylamide gel electrophoresis, and transferring and immobilizing the mixture onto a solid membrane of nitrocellulose or nylon by electroblotting. The loaded membrane is then incubated with an antibody raised against the protein of interest. The antibody-antigen complex formed on the membrane is then detected by a procedure that typically involves the application of a second antibody, raised against the first antibody, and to which an enzyme has been covalently linked. The insoluble reaction product generated by the enzyme action can then be used to indicate the position of the target protein on the membrane. The sensitivity of detection can be increased by amplification of the signal using either the biotin-streptavidin system or by chemiluminescence detection.
This classical procedure is very time consuming and labor intensive. For example, transferring the proteins to a membrane is generally a time consuming step and is typically done by capillary blotting or by the faster and more efficient methods of vacuum blotting or electrophoretic blotting.
More recently, new and faster microfluidic methods of performing biological assays in microfluidic systems have been developed, such as those described by the pioneering applications of Parce et al., “High Throughput Screening Assay Systems in Microscale Fluidic Devices” WO 98/00231 and in Knapp et al., “Closed Loop Biochemical Analyzers” (WO 98/45481; PCT/US98/06723). For example, high throughput methods for analyzing biological reagents, including proteins, are described in these applications.
Improved methods for performing western blot and affinity assays are, accordingly desirable, particularly those which take advantage of high-throughput, low cost microfluidic systems. The present invention provides these and other features by providing high throughput microscale systems for analyte detection, affinity purification, western blots, and the like, and many other features that will be apparent upon complete review of the following disclosure.